The present invention relates generally to a method of manufacturing plastic bags and more particularly to a novel method of manufacturing a gas permeable bag suitable for use in the cultivation of mushroom spawn which includes the apparatus upon which the method is performed.
U.S. Pat. No. 2,851,821 discloses mushroom spawn grown in a plastic bag. The bag is closed by turning the ends of the bag and forming a chimney, and it is sealed by placing a wad of cotton or the like in the chimney thus formed. In another embodiment, a tube is inserted in the top of the bag and the bag is gathered around the tube of the string. A filter plug is then placed in the tube.
Another method is described in U.S. Pat. No. 4,027,427 wherein the spawn is grown in a plastic bag provided with a temporary filter cover. This bag is provided with a removal closure mechanism for filling the bag and maintaining sterility during the processing steps.
U.S. Pat. No. 4,977,702 discloses a bag for the production of eatable mushrooms which is provided with a number of gas exchange surfaces or membranes which are impervious to outside microorganisms, thereby avoiding contamination of the nutrient substrate by outside microorganisms. Inoculation can be performed by injection of the inoculum in suspension through the plastic bag. The gas exchange membranes of the bag may be made of Dupont Tyvek.RTM. spun bonded polyolefin. U.S. Pat. No. 4,311,477 teaches a bag for cultivating mushrooms constructed, at least in part, from a micro-porous film having gas permeability, but which does not pass bacteria and infectious microbes.
The following U.S. and foreign references were identified as being relevant to the present invention:
U.S. Pat. No. 4,878,312 CHIMICU, U.S. Pat. No. 4,977,702 FORTIN ET AL.: EP No. 83-742416; JAPAN 2286-012; JAPAN 2-4673; GERMANY 3734-509-A; SWITZERLAND 647-209-A; GREAT BRITAIN 1,176,188 and GERMANY 148,436.
The production of mushrooms in plastic bags is well known in the art. Plastic as a material from which bags are made has been used advantageously in the field primarily because of the low manufacturing cost of such bags and the ease with which the bags are sterilized. However, maintaining an uncontaminated growing environment must be balanced with the ability to provide adequate airflow to the mushroom spawn. Accordingly, the need has developed a method for manufacturing such a bag and, appropriately, an apparatus for practicing the method thereon.